Method and apparatus for regenerating optical signals in an all-optical cross-connect switch

ABSTRACT

Methods, apparatus and systems for regenerating, monitoring and bridging optical signals through an optical cross-connect switch to provide increased reliability. A self testing method, apparatus and system for an optical cross-connect switch. An optical-to-electrical-to-optical converter (O/E/O) is provided in an optical cross-connect switch to provide optical-electrical-optical conversion. I/O port cards having an optical-to-electrical-to-optical converter are referred to as smart port cards while I/O port cards without an optical-to-electrical-to-optical converter are referred to as passive port cards. Test port/monitor cards are also provided for testing optical cross-connect switches. Methods, apparatus and systems for performing bridging, test access, and supporting redundant optical switch fabrics are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional United States (U.S.) patent application claims thebenefit of and is a divisional of U.S. patent application Ser. No.09/704,439 filed on Nov. 1, 2000 now U.S. Pat. No. 6,650,803 byinventors Rajiv Ramaswami, et al., entitled “METHOD AND APPARATUS FOROPTICAL TO ELECTRICAL TO OPTICAL CONVERSION IN AN OPTICAL CROSS-CONNECTSWITCH”, now allowed.

The parent patent application, U.S. patent application Ser. No.09/704,439, claims the benefit of U.S. Provisional Patent ApplicationNo. 60/162,936 entitled “OPTICAL CROSSCONNECT WITH OPTICAL TO ELECTRICALCONVERTERS” filed on Nov. 2, 1999 by inventor Rajiv Ramaswami; and alsoclaims the benefit of U.S. Provisional Patent Application No. 60/170,094entitled “OPTICAL CROSSCONNECT WITH BRIDGING, TEST ACCESS ANDREDUNDANCY” filed on Dec. 10, 1999 by inventors Rajiv Rarnaswami andRobert Ward; and also claims the benefit of U.S. Provisional PatentApplication No. 60/170,095 entitled “OPTICAL CROSSCONNECT WITH LOW-LOSSBRIDGING, TEST ACCESS, AND REDUNDANCY” filed on Dec. 10, 1999 byinventors Steven Clark and Rajiv Rarnaswami; and also claims the benefitof U.S. Provisional Patent Application No. 60/170,093 entitled “1+1OPTICAL PROTECTION USING OPTICAL CROSSCONNECTS” filed on Dec. 10, 1999by inventors Rajiv Ramaswami and Robert Ward; and also claims thebenefit of U.S. Provisional Patent Application No. 60/170,092 entitled“SIGNALING INTERFACE BETWEEN OPTICAL CROSSCONNECT AND ATTACHEDEQUIPMENT” filed on Dec. 10, 1999 by inventor Rajiv Ramaswami; and alsoclaims the benefit of U.S. Provisional Patent Application No. 60/186,108entitled “1:N PROTECTION BETWEEN CLIENTS AND ALL-OPTICAL CROSSCONNECTS”filed on Mar. 1, 2000 by inventors Kent Erickson, Subhashini Kaligotla,and Rajiv Ramaswami; and also claims the benefit of U.S. ProvisionalPatent Application No. 60/200,425 entitled “OPTICAL CROSSCONNECT SYSTEM”filed on Apr. 28, 2000 by inventors Rajiv Ramaswami, Steve Tabaska, andRobert Ward.

BACKGROUND OF THE INVENTION

Over the last few years, the demand for high-speed communicationnetworks has increased dramatically. In many situations, communicationnetworks are implemented with electrical interconnections. That is theinterconnections between nodes and networks are made using electroniccircuitry such as a transistor switch which blocks or passes electrons.One type of electrical interconnection is an electronic network switchwhich is well known. The application of electronic network switches tolocal area networks (LANs), metropolitan area networks (MANs) and widearea networks (WANs) is also well know. A network switch may stand aloneor be used in conjunction with or incorporated into other networkequipment at a network node. As desired levels of bandwidth andtransmission speed for communication networks increase, it will becomemore difficult for the electrical interconnections to satisfy theselevels.

One difficulty associated with electrical interconnections is that theyare sensitive to external electromagnetic interference. Morespecifically, electromagnetic fields that reside in the vicinity of theinterconnection lines induce additional currents, which may causeerroneous signaling. This requires proper shielding, which hamperedgeneral heat removal.

Another difficulty is that electrical interconnections are subject toexcessive inductive coupling, which is referred to as “crosstalk”. Toalleviate crosstalk, the electrical interconnections must be shielded orabide by fundamental rules of circuit routing so that they are set at adistance large enough to prevent neighboring signals from having anyadverse effect on each other, which would reduce network performance.

In lieu of electrical interconnections switching electrons or a voltageand current, optical interconnections offer a solution to thedifficulties affecting conventional electrical interconnections. Opticalinterconnections switch photons or light ON and OFF at one or morewavelengths to provide signaling. An advantage to opticalinterconnections is that they are not as susceptible to inductive oreven capacitive coupling effects as electrical interconnections. Inaddition, optical interconnections offer increased bandwidth andsubstantial avoidance of electromagnetic interference. This potentialadvantage of optics becomes more important as the transmission ratesincrease and as the strength of mutual coupling associated withelectrical interconnections is proportional to the frequency of thesignals propagating over these interconnections.

Albeit local or global in nature, many communications network featureselectronic switching devices to arbitrate the flow of information overthe optical interconnections. Conventional electronic switching devicesfor optical signals are designed to include hybrid optical-electricalsemiconductor circuits employing photodetectors, electrical switches,optical modulator or lasers. The incoming optical signals are convertedto electrical signals by photodetectors. The electrical signals areamplified and switched by electronic switches to the appropriate outputand then converted into optical signals by lasers. One disadvantageassociated with a conventional electronic switching device is that itprovides less than optimal effectiveness in supporting high datatransmission rates and bandwidth.

An alternative approach is to develop an optical cross-connect systemwhich performs switching operations of light pulses or photons (referredto generally as “light signals”) without converting and reconvertingsignals between the optical domain to the electrical domain. However,switching light or photonic signals is different and introducesadditional challenges over conventional electrical switching. One ofthese challenges is fault protection. Failure modes in an optical systemtypically include a faulty component which can be catastrophic severinga communication channel or causing periodic generation of bit errors.

Another challenge to an optical cross-connect system, is generatingstatus information regarding the data transmission status of the lightor optical signals through the optical cross-connect. Yet anotherchallenge in an optical cross-connect system is in creating a reliableoptical cross-connect switch. Still yet another challenge in an opticalcross-connect system is the ability to completely test such a system.These are challenges because the light or optical signals are not in anelectrical form in an all optical cross-connect system and the dataformat and the data rate of individual channels is unknown to an alloptical cross-connect system. Each and every channel can have theirlight pulses converted into electrical pulses for monitoring but this isan expensive solution which requires an optical to electrical conversionfor each and every channel.

SUMMARY OF THE INVENTION

The present invention is briefly described in the claims that followbelow.

Briefly, the present invention provides methods, apparatus and systemsfor performing optical-electrical-optical conversion in an opticalcross-connect switch. An optical-to-electrical-to-optical converter(O/E/O) is provided in an optical cross-connect switch to provide theoptical-electrical-optical conversion. I/O port cards having anoptical-to-electrical-to-optical converter are referred to as smart portcards while I/O port cards without an optical-to-electrical-to-opticalconverter are referred to as passive port cards. Test port/monitor cardsare also provided for testing optical cross-connect switches. Methods,apparatus and systems for performing bridging, test access, andsupporting redundant optical switch fabrics are also disclosed. Methods,apparatus and systems for regenerating, monitoring and bridging opticalsignals through an optical cross-connect switch to provide increasedreliability are also disclosed. A self testing method, apparatus andsystem for an optical cross-connect switch is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will becomeapparent from the following detailed description of the presentinvention in which:

FIG. 1 is a simplified overview of an embodiment of an opticalcross-connect switching system.

FIG. 2 is a first exemplary embodiment of an optical cross-connectswitching system of FIG. 1.

FIG. 3 is an exemplary embodiment of the optical fiber switch matricesforming an optical fiber switch fabric of FIG. 2.

FIG. 4 is an exemplary embodiment of mirror arrays forming an opticalfiber switch matrix of FIG. 3.

FIG. 5 is an exemplary embodiment of an I/O subsystem featuring aplurality of I/O port modules.

FIG. 6 is an exemplary embodiment of a data path for the transfer oflight between I/O port modules and multiple fiber optical switch fabricsof FIG. 2.

FIG. 7 is an exemplary embodiment of a control path featuring theinterconnections between the I/O port module and servo modules.

FIG. 8 is an exemplary embodiment of the I/O port module of FIGS. 6 and7 illustrating a data propagation circuit and a control circuit.

FIG. 9 is an exemplary embodiment of multiple ports of I/O modules incommunication with optical switches controlled by servo modules.

FIG. 10 is an exemplary embodiment of an I/O port configured as a testaccess port.

FIG. 11 is an exemplary embodiment of a servo module of the opticalcross-connect switching system of FIG. 1.

FIG. 12 is an exemplary block diagram of a redundant architecture of theoptical cross-connect switching system of FIG. 1.

FIG. 13 is a block diagram illustrating an out-of-band signalinginterface between an optical cross-connect switch and attached networkequipment.

FIG. 14 is a block diagram illustrating a decentralized signalinginterface between an optical cross-connect switch and attached networkequipment.

FIG. 15 is a block diagram of an optical cross-connect switch havingvarious port cards including passive port cards and smart port cardshaving optical-electrical-optical converters.

FIG. 16 is a block diagram of an optical cross-connect switch having aone and two tiered port card arrangement with smart port cards havingoptical-electrical-optical converters coupled to passive port cards.

FIG. 17 is a block diagram of an optical cross-connect switch includingport cards providing bridging in an optical switch fabric.

FIG. 18 is a block diagram of an alternate optical cross-connectincluding port cards providing bridging in an optical switch fabric.

FIGS. 19A-19G are block diagrams of an optical cross-connect switchincluding smart port cards and/or passive port cards to provide bridgingusing a redundant optical switch fabric and testing/monitoring using atest port/monitoring card.

FIG. 20 is a block diagram of an optical cross-connect switch includinga test port/monitoring card to provide self-testing/monitoring of theoptical switch fabrics of an optical cross-connect switch havingredundant optical switch fabrics.

Like reference numbers and designations in the drawings indicate likeelements providing similar functionality. A letter or prime after areference number designator represents another or different instance ofan element having the reference number designator.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances well known methods,procedures, components, and circuits have not been described in detailso as not to unnecessarily obscure aspects of the present invention.

In the following description, certain terminology is used to describevarious features of the present invention. For example, a “module”includes a substrate normally formed with any type of material ormaterials upon which components can be attached such as a printedcircuit board or a daughter card for example. Examples of a “component”include an optical switch, a processing unit (e.g., Field ProgrammableGate Array “FPGA”, digital signal processor, general microprocessor,application specific integrated circuit “ASIC”, etc.), splitters and thelike. A “splitter” is an optical component that performs a bridgingoperation on an input light signal by splitting that light signal intotwo or more output light signals. Each module features one or moreinterfaces to transport information over a link. A “link” is broadlydefined as one or more physical or virtual information-carrying mediumsthat establish a communication pathway such as, for example, opticalfiber, electrical wire, cable, bus traces, wireless channels and thelike. “Information” can be voice, data, address, and/or control in anyrepresentative signaling format such as light signals (e.g., lightpulses or photons).

I. General Architectural Overview

Referring to FIG. 1, an exemplary embodiment of a simplified overview ofan optical cross-connect switching system 100 is shown. Herein, theoptical cross-connect switching system 100 comprises three basic units:a switch subsystem 110, a switch control subsystem 120 and aninput/output (I/O) subsystem 130. In one embodiment, the modulararchitecture of the switch subsystem 110, by a method of havingreplaceable optical switch cores, provides for switch subsystemmaintenance in the event of failure within the switch subsystem 110. Itis conceivable that further modularity could be achieved by havingreplaceable subsections within, thus providing for switch matrixmaintenance in the event of failure within a switch matrix itself. Themodular architecture of both the switch control subsystem 120 and theI/O subsystem 130, each handling a small number of I/O ports in thesystem 100, provides scalability to the optical cross-connect switchingsystem 100. Thus, additional I/O ports may be subsequently added to theoptical cross-connect switching system 100 by adding or removinginput/output (I/O) port modules (described below).

The switch subsystem 110 includes optical switches for routing lightsignals. In one embodiment, the optical switches forming the switchsubsystem 110 are micro-machined mirrors; however, it is contemplatedthat other switch fabrics may be used such as liquid crystal technology.The I/O subsystem 130 receives external light signals 140 and transfersthese signals to the switch subsystem 110. The switch control subsystem120 controls the configuration of the switch subsystem 110 (e.g., mirrororientation) and performs certain monitoring functions. Theinterconnectivity between the switch subsystem 110, the switch controlsubsystem 120 and the I/O subsystem 130 includes redundancy so that noequipment failures would cause complete disablement of the system 100.

Referring now to FIG. 2, a first exemplary embodiment of an opticalcross-connect switching system 100 is shown. In general, the opticalcross-connect switching system 100 is a matrix-based opticalcross-connect with associated I/O port modules. More specifically, theoptical cross-connect switching system 100 is collectively formed by aplurality of platforms 205, 206 and 207 in communication with eachother, although the implementation of the switching system 100 as asingle platform is another embodiment. Herein, each platform 205, 206and 207 includes a frame 210 (e.g., a rack) that physically supports I/Oport modules forming the I/O subsystem 130 as well as servo modules,servo control modules and/or network control modules of the switchcontrol subsystem 120. The modules are arranged either horizontally orvertically within each platform 205, 206 and 207 and can be individuallyremoved or installed without interfering with immediately adjacentmodules. In addition, the frame 210 may also physically support one ormore optical switch cores, which may also generally be referred to as“switch fabric,” of the switch subsystem 110.

As shown in this embodiment, the first platform 205 comprises (i) aplurality of I/O port modules 215 associated with the I/O subsystem 130of FIG. 1, (ii) a plurality of servo modules 225 and a managementcontrol subsystem (MCS) 235 associated with switch control subsystem 120of FIG. 1, and (iii) a first (primary) optical switch core 240associated with switch subsystem 110 of FIG. 1. Similarly, the secondplatform 206 comprises a plurality of additional I/O port modules 245, aplurality of (redundant) servo modules 250, a management controlsubsystem 255, and a second (redundant) optical switch core 260. Thethird platform 207 comprises a plurality of servo modules 265 thatcontrol various mirrors of the first and second optical switch cores 240and 260, which correspond to additional ports associated with I/O portmodules 245. Additionally, a light path test signal generator(s), alight path signal monitor(s), circuit breakers and/or alarm visualindication 270 may be located within the third platform 207. Forclarity, the elements forming the first platform 205 are described sincethese elements may be found in the second and/or third platforms 206 and207.

As shown in both FIGS. 2-4, the first optical switch core 240 includes afirst optical switch matrix 241 and a second optical switch matrix 242.These matrices 241 and 242 are collectively positioned to route lightsignals 250 between a port of a source I/O port module 215 _(s) (“s” isa positive whole number) and a port of a destination I/O port module 215_(d) (“d” is a positive whole number), both modules located in any ofthe platforms 205, 206 and 207 as shown in detail in FIG. 3. Although atwo-bounce routing technique is shown, it is contemplated that otherlight routing techniques may be used including a three-bounce routingtechnique in which a second bounce mirror 202 optionally shown in FIG. 3is positioned to assist in routing light signals from one optical switchmatrix to another.

As shown in FIG. 4, one embodiment for each of the optical switchmatrices 241 and 242 includes multiple arrays 300 of micro-machinedmirrors. Each mirror (e.g., mirror 310) features a mirrored surface 311and torsional flexures 320 and 330 that enable the mirror 310 to adjustits physical orientation to reflect incoming light signals in anyselected direction. Herein, both the first and second optical switchmatrices 241 and 242 include Q micro-machined mirrors, where “Q” is lessthan or equal to the maximum number of I/O ports that can be supportedby the optical cross-connect switching system 100. For this embodiment,“Q” is greater than or equal to 64 but less than or equal to 1152(64≦Q≦1152). However, the present invention is not limited to anymaximum number of mirrors or I/O ports. It is contemplated, however,that the number of mirrors employed within the first and second opticalswitch matrices 241 and 242 may differ.

As generally shown in FIGS. 2, 5 and 6, the plurality of I/O portmodules 215 features two groups 216 and 217 of I/O port modules. Eachgroup, such as group 216 or 217 for instance, includes up to seventy-two(72) quad-port I/O port modules as shown in FIG. 5 that receive powerfrom one or more power supply modules denoted herein as “PSM”. Thecomponents forming an I/O port module is described below and shown inFIGS. 8 and 9. Thus, each I/O port module, such as I/O port module 215_(s) for example, features an external interface 400 for a plurality ofI/O ports 410 (e.g., four I/O ports). An I/O port 410 features a duplexsocket that is adapted to receive a duplex pair of optical fiber links,one optical fiber link routes a light signal to the I/O port 410 whilethe other routes light signals from the I/O port 410. This supportbi-directional optical connections. There is a small percentage (e.g.,less than 15%) of these I/O ports, however, that may be assigned as testaccess ports as described below.

Moreover, as shown in FIG. 6, upon receiving an incoming light signalover an optical fiber link 420, the I/O port module 215 _(S) performs abridging operation by splitting the incoming light signal into multiple(two or more) bridged light signals for routing to the first and secondoptical switch cores 240 and 260. The bridged light signals are routedthrough an internal optical interface 425 featuring optical fiber ribbonlinks 430 and 440. For this embodiment, the “optical fiber ribbon links”are ribbon cables having multiple optical fiber lines (e.g., two linesfrom each I/O port). The first optical switch core 240 provides aprimary optical path. The second optical switch core 260 provides aredundant optical path in the event the first optical switch core 240 isnot operating properly. The optical switch cores 240 and 260 route thebridged light signals to a selected port of a destination I/O portmodule (e.g., I/O port module 215 _(d)) via optical fiber ribbon links450 and 460.

Upon receiving light signals from both the first and second opticalswitch cores 240 and 260, the I/O port module 215 _(s) provides smallpercentage optical tap signals of the received light paths to therespective servo modules, which in turn determine light signal quality.The respective servo modules will convey light signal quality for eachrespective light path to the I/O port module, using a digital protocolover an electrical communication link 505 to the I/O port module asshown in FIG. 7. The I/O port module 215 _(s) will in turn, determine(i.e. select) which light signal has the higher signal quality andoutputs that signal via interface 400. In most cases, the signal qualityof the two light paths presented to the I/O port module will be of thesame signal quality and may have a relatively low optical loss ofapproximately seven decibels (7 dB) or less.

Referring now to FIGS. 2 and 7, each servo module 225 is configured toreceive optical tap signals from one or more I/O port modules. Herein,servo module 225 _(i) is configured to receive optical tap signals vialink 500 from I/O port module 215 _(s). These optical tap signalsprovide feedback to indicate a percentage of the bridged light signalsand also allow for light to be injected under certain conditions. Inresponse to receiving optical tap signals via link 500, the servo module225 _(i) provides mirror control signals over link 510 to the firstoptical switch core 240. The mirror control signals are routed via aunique communication path to an optical switch (e.g., a micro-machinedmirror) and are associated with the port of the I/O port module 215 _(s)through which the incoming light signal was routed. The mirror controlsignals are used for proper adjustment of the physical orientation ofthe mirror.

The I/O port module 215 d provides optical tap signals over link 530 toservo module 225 _(j). In response to receiving the optical tap signalsfrom I/O port module 215 _(d), the servo module 225 _(j) provides mirrorcontrol signals via link 540 to the first optical switch core 240. Themirror control signals are routed via a unique communication path to amicro-machined mirror associated with a selected port of the I/O portmodule 215 _(d) from which the light signal would be output. Herein,sensing the optical tap (feedback) signals, the servo module 225 _(j)determines the light signal quality and conveys light signal qualityinformation for each light path using a digital protocol over(electrical) link 535. Thereafter, the I/O port module 215 d chooses theselected port (i.e. port having the best light signal quality).

Collectively, the optical tap signals, mirror control signals and lightsignal quality information, which are routed over links 500, 510, 530,540, 505 and 535, are used by servo modules 225 _(i) and 225 _(j) foradjustment of the physical orientation of mirrors to make a connectionbetween I/O port module 215 _(s) and 215 _(d).

Additionally, I/O port modules 215 _(s) and 215 _(d) also transferoptical tap signals via links 520 and 550, respectively. Similar to theabove description, these optical tap signals establish the redundantoptical path by altering the physical orientation of one or moremicro-machined mirrors of the second optical switch core 260 usingmirror control signals over links 560 and 570 and light signal qualityinformation via links 525 and 555.

In the event that no optical power is presented to the I/O port module215 _(s), a substitute light signal may be injected from the servomodule 225 _(i) via link 500. An alignment laser may be used as shown inFIG. 11 described below. This process of light substitution allows forconnection establishment and verification when no input light is presentto the I/O port module 215 _(s). The substitute light source can bewithin the same wavelength range (e.g. 1100 nanometers “nm”-1700 nm) asthe allowed input light signal range. In one embodiment, the lightsource or method of injection would be chosen to not interfere withattached equipment's select operational wavelength range. Choosing adifferent wavelength source on the servo module and/or a wavelengthspecific splitter and/or filter on the I/O port module could do thisparticular embodiment.

The management control subsystem 235 (see FIG. 2) enables communicationsbetween two or more servo modules placed within the same or differentplatforms. The management control subsystem 235 includes at least oneservo control module 236 and an optional network control module 238. Inone embodiment, the servo control module (SCM) 236 ensures communicationbetween at least servo modules 225 _(i) and 225 _(j) that controlmirrors associated with the first optical switch core 240. The networkcontrol module (NCM) 238 manages the execution of connectionconfigurations for the whole cross-connect switching system and ensurescommunications between multiple servo control modules 236 and 237. Thesame architecture is used to control optical switches within the secondoptical switch core 260 as shown.

II. General Architecture of the I/O Port Modules

Referring now to FIGS. 8 and 9, an exemplary embodiment of an I/O portmodule (e.g., I/O port module 215 _(s)) and its communications overoptical switch cores 240 and 260 is shown. I/O port module 215 _(s)includes a data propagation circuit 600 for each I/O port and a controlcircuit 670. Thus, in the event that the I/O port module 215 _(s) isconfigured with four I/O ports, four data propagation circuits areimplemented on the I/O port module 215 _(s) as represented. Only thedata propagation circuit 600 for one of the I/O ports of I/O port module215 _(s) (e.g., i^(th) I/O port) is shown in detail for clarity sake.

In one embodiment, the data propagation circuit 600 comprises an opticalswitch 610, a (passive) splitter 620 and a plurality of tap couplers 630₁-630 ₄. The plurality of tap couplers 630 ₁-630 ₄ correspond to thepairs of optical fibers found in optical fibber ribbon links 430 and440. The control circuit 670 comprises a programmable memory 680, aprocessing unit 685 and status identification components 690.

As shown, each port of the I/O port module 215 _(s) supports full-duplexcommunications. Thus, an incoming light signal 606 received over port605 is routed to the splitter 620. The splitter 620 effectively performsa bridging operation by splitting the incoming light signal 606 intobridged light signals 625, which collectively have the same power level(energy) as the light signal 606. In one embodiment, when the splitter620 is a 50/50 splitter, the bridged light signals 625 have equal powerlevels. However, it is contemplated that splitter 620 may producebridged light signals 625 having disproportionate power levels.

The bridged light signals 625 are routed through the tap couplers 630 ₁and 630 ₂. Attached to servo module 225 _(i) and servo module 225 _(i+1)via optical tap links 500 and 520, the tap couplers 630 ₁ and 630 ₂ areused to monitor the power level of light signals 635 and 636 propagatingthrough optical fiber ribbon links 430 and 440 (referred to as “outgoinglight signals”). This enables the servo modules 225 _(i) and 225 _(i+1)to verify the connectivity of the splitter 620 to optical fiber ribbonlinks 430 and 440 and to detect unacceptable variances in opticalperformance of the light signal. As shown for this embodiment, the tapcouplers 630 ₁ and 630 ₂ may separate the bridged light signals intosignals having disproportionate power levels in order to maximize thepower levels of the outgoing light signals propagating through opticalfiber ribbon links 430 and 440. For example, where the tap couplers 630₁ and 630 ₂ may operate as 90/10 splitters, the outgoing light signals635 and 636 have ninety (90%) of the total power level of the bridgedlight signal while the tap optical signals 640 and 641 have only tenpercent (10%).

Referring to FIG. 8, tap couplers 630 ₃ and 630 ₄ are configured toreceive incoming light signal 650 and 655 via optical fiber ribbon links430 and 440, respectively. The tap couplers 630 ₃ and 630 ₄ effectivelyseparate the light signals 650 and 655 into corresponding pairs of lightsignals having disproportionate power levels (e.g., signals 661, 662 and663, 664). Signals 662 and 664 having the lower power level are providedto the servo module 225 _(i) and servo module 225 _(i+1) via links 500and 520 for monitoring the power levels of the light signals 661 and663, without the light signals 661 and 663 experiencing substantialsignal degradation. The signals 662 and 664 may be light signals thatundergo O/E conversion at the I/O port module 215 _(s) or at the servomodules 225 _(i) and 225 _(i+1) as shown in FIG. 11. The tap couplers630 ₃ and 630 ₄ are shown as 90/10 splitters; however, tap couplers 630₃ and 630 ₄ may be any selected ratio, including 50/50.

The light signals 661 and 663 are routed to the optical switch 610 of adestined I/O port. The control circuit 650 on the I/O port module 215_(s) determines which of the pair of light signals 661 and 663 has thebest signal quality based on conveyed light signal quality informationfrom the servo modules via links 505 and 525 as briefly described below.Parameters used to determine light signal quality include measuredoptical signal intensity/power, extinction ratio, and the like. Thelight signal quality information to the I/O port module may be conveyedas failed due to the servo module service operations, high bit errorrate, an external light path has failed, and the like. The light signal661 or 663 with the best signal quality is output through the I/O port605. Of course, it is contemplated that the light signal outputoperations described for I/O port i are applicable to I/O port j asshown.

It is contemplated that an I/O port of the I/O port module 215 _(s) maybe configured as a test access port. A “test access port” is an I/O portthat is used for monitoring light signals routed through another port.Normally, the test access port receives a portion of the power level ofa light signal routed through a selected optical switch (e.g.,micro-machined mirror). For example, as shown in FIG. 10, an I/O port218 of the I/O port module 215 _(s) is configured for coupling with amonitoring device 219 (e.g., a bit error rate “BER” monitor incombination with an optical-electrical “O/E” converter, etc.) to monitora power level of a light signal routed to the i^(th) I/O port from anoptical switch.

Referring back to FIG. 8, the control circuit 670 comprises theprogrammable memory 680 in communication with the processing unit 685(e.g., FPGA). The programmable memory 680 contains software and otherinformation used by the processing unit 685 to provide selection of thebest quality signal based on digital electrical signaling from servomodule 225 _(i) and servo module 225 _(i+1) over links 505 and 525,respectively. Also, programmable memory 680 includes information used bythe processing unit 685 to control the state of the statusidentification components 690 (e.g., light emitting diodes “LEDs”). Thestate of the status identification components 690 identifies (1) whethereach I/O port is operational and/or (2) whether the I/O port module isoperational. The processing unit 685 is further in communications withoptical switches of each data propagation circuit employed in the I/Oport module 215 _(s) in order to receive switch status signals andprovide switch control signals. As shown for clarity, processing unit685 provides optical switch 610 with switch control signals forreceiving switch status signals and selecting either light signal 661 orlight signal 663.

III. General Architecture of the Servo Modules

Referring now to FIG. 11, an exemplary embodiment of the servo module(e.g., servo module 225 _(i)) is shown. In one embodiment, the servomodule 225 _(i) comprises two separate modules in communication overconnectors 705 and 790. These separate modules are referred to as an“optical detector module” 700 and a “servo mirror control module” 750.

The optical detector module 700 comprises a first processing unit 710,memory 715, a plurality of detection/modulation (DM) circuits 716 andstatus identification components 717. As shown, the optical detectormodule 700 features sixteen (16) DM circuits 716 to support four (4)quad-port I/O port modules. Each DM circuit 716 includes ananalog-to-digital (A/D) converter 720, a laser 725, optical-electrical(O/E) detectors 730 and 731, and optional amplifiers 735 and 736.

The servo mirror control module 750 comprises a second processing unit755, a memory 760, a plurality of mirror signal detection and generation(SDG) circuits 761, a third processing unit 775 and statusidentification components 795. The SDG circuits 761 correspond in numberto the DM circuits 716 of the optical detector module 700. Each SDGcircuit 761 features an A/D converter 765, a digital-to-analog (D/A)converter 770, hinge position sensors 780-781 and high voltage (HV)mirror drivers 785-786.

As shown in FIG. 11, the optical detector module 700 is removablycoupled to the servo mirror control module 750. This allows the opticaldetector module 700 to be “hot swapped” from a backplane, which featuresconnectors 705 and 790 connecting the optical detector module 700 to theservo mirror control module 750, without disrupting the servo mirrorcontrol module's 750 ability to hold the mirrors in their existingpositions for an extended period of time. This “hot swapping” of theoptical detector module 700 allows for repair or upgrade of the opticaldetector module 700. Optical detector module 700 receives optical tap(feedback) signals 640 and 662 from one or more I/O port modules (e.g.,I/O port module 215 _(s) via link 500) and can transmit optical controlsignals 726 from the laser 725 for alignment of light signalstransferred between two I/O port modules. The optical tap signal 640 isbased on an input light signal that is routed to the switch fabric.

More specifically, with respect to servo module 225 _(i), the O/Edetectors 730 and 731 are coupled to tap couplers 630, and 6303 of FIGS.8-9. More specifically, the O/E detectors 730 and 731 are configured todetect incoming, optical tap signals 640 and 662, convert the opticaltap signals 640 and 662 into corresponding electrical control signalsmeasuring a power level of the outgoing light signal, and optionallyroute the electrical control signals to corresponding amplifiers 735 and736. The (amplified) electrical control signals are provided to the A/Dconverter 720. The A/D converter 720 converts the electrical controlsignals into measured power sense signals 644 of a digital form. Themeasured power sense signals 644 are provided to the first processingunit 710.

Herein, the first processing unit 710 may perform a number of operationsbased on the electrical control signals such as threshold crossing, LOSintegration, input/output power ratio analysis and the like. Softwareand other information necessary for performing these operations may beobtained from the memory 715 by the first processing unit 710. Herein,memory 715 can be non-volatile memory such as non-volatile random accessmemory, electrically erasable programmable read only memory (EEPROM) andthe like.

The optical detector module 700 includes multiple status identificationcomponents 717 (e.g., light emitting diodes “LEDs”). A first LED 718identifies whether any operational faults associated with the servomodule 225 _(i) have occurred. A second LED 719 indicates when theoptical detector module 700 is in service.

Referring still to FIG. 11, in this embodiment, the servo mirror controlmodule 750 comprises the second processing unit 755 that is coupled toboth the first processing unit 710 and the third processing unit 775.For instance, in order to adjust the switch fabric in response to themeasured power sense signals 644, the second processing unit 755receives information representative of the measured power sense signalsfrom the first processing unit 710 via connectors 705 and 790. Thesecond processing unit 755 further receives information representativeof measured power sense signals for the light signal at a targeted I/Oport. This information is provided by the SCM 236 over link 580 via thethird processing unit 775. This assists in reducing errors in adjustingthe torsional flexures of the mirrors.

Upon receipt of these measured power readings, the second processingunit 755 controls a particular SDG circuit corresponding to a mirrorassociated with the I/O port over which the tapped light signal wasrouted. The control involves slight mirror orientation adjustments ifthe power level readings differ substantially.

In particular, a first hinge position sensor 780 senses a position of amirror via link 510 from the first optical switch core 240. The sensedposition signal is routed to the A/D converter 765, which issubsequently placed in a digital format before routing to the secondprocessing unit 755. When the servo module 225 _(i) is adjusting theswitch fabric, the second processing unit 755 transfers mirror controlsignals to the D/A converter 770. The mirror control signals are routedto HV driver 785 and applied to a selected mirror of the first opticalswitch core in order to adjust the amount of torsional flexure along afirst dimensional plane (e.g., X-axis). This is accomplished to minimizethe loss experienced by the light signal.

A second hinge position sensor 781 senses a position of a mirror for thefirst optical switch core along a second dimensional plane (e.g.,Y-axis). The sensed position signal is routed to the A/D converter 765,which is subsequently placed in a digital format before routing to thesecond processing unit 755. When the servo module 225 _(i) is adjustingthe switch fabric, the second processing unit 755 transfers mirrorcontrol signals to the D/A converter 770. The mirror control signals arerouted to HV driver 786 and are applied to the selected mirror of thefirst optical switch core in order to adjust the amount of torsionalflexure along the second dimensional plane. The specifics of the hingeposition sensors 780 and 781 are described in a PCT application entitled“Micromachined Members Coupled for Relative Rotation By TorsionalFlexure Hinges” (International Publication No. WO 00/13210) published onor around Mar. 9, 2000.

In another embodiment, when I/O port module 215 _(s) is the destinationof a light signal, the second processing unit 755 receives informationrepresentative of the measured power sense signals associated with theoptical tap signal 662 that has been analyzed by the first processingunit 710. The optical tap signal 662 is based on an output light signalbeing routed from an I/O port. In this situation, the third processingunit 775 receives information associated with the measured power sensesignals from a source I/O port as reported by SCM 236 over link 580.

IV. Redundant Architecture of the Optical Cross-connect Switching System

Referring now to FIG. 12, a block diagram of an alternative embodimentof the architecture of the optical cross-connect switching system ofFIG. 1 is shown which includes redundant protection capabilities.Redundancy is desired in order to increase the reliability of such anoptical cross-connect switching system. Aside from the I/O port modules,all other modules are duplicated to obtain the desired redundancy. Thus,it is necessary for light signals from a source I/O port module 215 _(s)to be routed to a destination I/O port module 215 _(d) through twooptical paths, namely a primary optical path 800 using a first opticalswitch core 240 and a redundant optical path 810 using a second opticalswitch core 260.

With respect to the primary optical path 800, a servo module 225 _(i) isconnected to both the source I/O port module 215 _(s) and the firstoptical switch matrix (not shown) of the first optical switch core 240.In particular, the servo module 225 _(i) controls the physicalorientation of a mirror of the first optical switch matrix thatcorresponds to the source I/O port module 215 _(s). To establish andmaintain the primary optical path 800 for the light signal, the servomodule 225 _(i) needs to communicate with other servo modules such asservo module 225 _(j). Thus, a servo control module (SCM) is implementedto support such communications, possibly through a time-slot switchingarrangement.

As shown, the SCMs 236 ₁-236 ₂ are also duplicated so that each servomodule 225 is connected to at least two SCMs 236 ₁-236 ₂. Thus, in theevent that the SCM 236 ₁ fails, the primary optical path 800 remainsintact because communications between the servo modules 225 _(i) and 225_(j) are maintained via redundant SCM 237 ₁. The transfer isaccomplished by temporarily halting the adjustment of (i.e. freezing)the mirrors inside the first optical switch core 240 while control istransferred from SCM 236 ₁ to SCM 237 ₁. The SCMs 236 ₁ and 237 ₁associated with the first optical switch core 240 are in communicationvia a network control modules (NCMs) 238 ₁ and 238 ₂ for example.

With respect to the redundant optical path 810, a servo module 225_(i+1) is connected to both the source I/O port module 215 _(s) and oneor more mirror(s) of a first optical switch matrix (not shown) of thesecond optical switch core 260. Another servo module 225 _(j+1) isconnected to both the destination I/O port module 215 _(d) and one ormore mirror(s) of a second optical switch matrix (not shown) of thesecond optical switch core 260. The orientation of these mirrorsproduces the redundant optical path 810.

To establish and maintain the redundant optical path 810 for the lightsignal, a SCM 236 ₂ may be implemented with a dedicated time-slotswitching arrangement in order to support continuous communicationsbetween the servo module and another redundant servo module associatedwith the destination I/O port module. As shown, the SCM 236 ₂ is alsoduplicated so that each servo module 225 _(i+1) and 225 _(j+1) isconnected to at least two SCMs 236 ₂ and 237 ₂. Thus, the redundantoptical path 810 is maintained even when one of the SCMs 236 ₂ and 237 ₂fails. The SCMs 236 ₂ and 237 ₂ associated with the second opticalswitch core 260 communicate via the first NCM 238 ₁ and the second NCM238 ₂, respectively. The second NCM 238 ₂ is in communication with thefirst NCM 238 ₁ to allow all SCMs and servo modules to communicate forcoordination of the primary optical path 800 and the redundant opticalpath 810.

V. Signaling Interface

The present invention includes alternate embodiments for realizing asignaling interface between optical cross-connect switches and attachednetwork equipment (ANE). Referring to FIG. 13, optical cross-connectswitches (OXCs) 1300 are deployed in a telecommunications network. Anoptical cross-connect switch can also be referred to herein as opticalcross-connect switching system, OXC, or optical cross-connect. Attachedto the optical cross-connect switches in a telecommunications network isone or more pieces of attached network equipment (ANE) 1302. Theattached network equipment (ANE) 1302 includes telecommunication networkdevices such as a wavelength division multiplexed (WDM) line terminals,SONET add/drop multiplexers, internet protocol (IP) routers, additionaloptical cross-connect switches and Asynchronous Transfer Mode (ATM)switches which are also collectively referred to as client equipment.WDM line terminals provide interconnection between sites and are alsoterminating devices included in SONET add/drop multiplexers, internetprotocol (IP) routers, or Asynchronous Transfer Mode (ATM) switches. Thepresent invention establishes a signaling interface between the opticalcross-connects 1300 and attached network equipment (ANE) 1302.

There are a number of reasons for establishing a signaling interfacebetween the optical cross-connects 1300 and attached network equipment(ANE). One reason is to allow the other network equipment in thetelecommunications network to provision connections through the OXC. Itis very desirable to allow other equipment to set up a connectionthrough the OXC in an automated manner, rather than manuallyprovisioning such connections. Another reason is to provide real-timeperformance monitoring and other management information to the opticalcross-connects 1300 from the attached network equipment 1302. Byproviding a signaling interface where performance information isprovided back to the optical cross-connects 1300, expensive monitoringelements are not needed inside the optical cross-connects 1300 and costsare saved. The attached network equipment usually already haveelectronic components for monitoring signals, such asoptical-to-electrical-to-optical converters (OEOs or O/E/Os), in orderto extract such information from optical signals. Thus, the electronicsfor monitoring do not need to be duplicated inside the opticalcross-connects 1300 when they are already provided in the attachednetwork equipment 1302. Instead the optical cross-connects 1300 canobtain the real-time performance monitoring and other managementinformation from the other network equipment that is attached to theoptical cross-connects 1300 through a signaling channel. Another reasonto establish a signaling interface is so that the attached networkequipment 1302 can obtain monitoring and other management informationreal-time from the optical cross-connects 1300. The opticalcross-connects 1300 can similarly monitor received optical signals onits input ports and provide information back to the attached networkequipment 1302. Preferably, the optical cross-connects 1300 only monitorthe optical power of the received optical signals by tapping off a smallpercentage of the energy of the optical signal and useoptical-to-electrical converters (OEs or O/Es) to determine the opticalpower without using O/E/Os.

FIG. 13 illustrates a block diagram of an out-of-band signalinginterface between an optical cross-connect switch 1300 and attachednetwork equipment 1302. The signaling interface is realized by using anout-of-band communication channel over a network 1304 which may also bereferred to as an out-of-band signaling channel. In-band communicationchannels are those used by the optical cross-connect switch 1300 toswitch data signals on the one or more data signals lines 1306A-1306N.An out-of-band communication channel is a communication channel otherthan that used by the optical cross-connect switch 1300 to switch itsdata signals on the data lines 1306A-1306N. The in-band communicationchannels used to switch data signals on the data lines 1306A-1306N bythe optical cross-connect switch 1300 are light signals, also referredto as photonic signals or optical signals, that are carried in opticalfibers. The data lines 1306A-1306N are not used for the signalinginterface because these lines carry high-bandwidth signals. To convertoptical signals in the optical domain into electrical signals in theelectrical domain to extract signaling information is a very expensiveprocess. Indeed, a major reason for using an all-optical cross-connectis to avoid converting signals from the optical domain to the electricaldomain. The out-of-band signaling channel is provided on a network 1304such as a LAN, a MAN, the internet or other WAN. Each of the data lines1360A-1306N is bi-directional to provide duplex data communicationchannels. The data lines 1306A-1306N in one embodiment include at leasttwo optical fibers for data flow in each direction between the opticalcross-connect switch and the attached network equipment 1402 to providefull duplex data communication channels. In another embodiment, each ofthe data lines 1306A-1306N is a single optical fiber to providebi-directional signal flow in both directions and can be full or halfduplex data communication over a single optical fiber. Full duplex isaccomplished over a single optical fiber by transmitting and detectingsignals in the single optical fiber at each end. [NOTE—IS THIS CORRECTTO SAY FOR FULL DUPLEX OVER A SINGLE FIBER. WE HAVE BEEN TRYING TO MOVETOWARDS SAYING “TRANSPORT” SO WHEN AN OPTICAL RECEIVE AND TRANSMITTERARE NOT PROVIDED. PLEASE COMMENT. WEA] The network 1304 also provides abi-directional out-of-band signaling channel so that signals can bereceived and transmitted in each direction between the opticalcross-connect switch and the attached network equipment 1402 and othernetwork equipment coupled to the network 1304. [IN THIS CASE IT SHOULDBE OK TO SAY TRANSMIT AND RECEIVE BECAUSE IT'S THE SINGALING INTERFACE.CORRECT?] The out-of-band signaling channel can be either full duplex orhalf duplex in providing bi-directional data communication.

Data signals from the optical cross-connect switch 1300 on the datalines 1306A-1306N are coupled into the attached network equipment 1302.The data lines 1306A-1306N are a light transmission media, such asoptical fibers, coupled between the optical cross-connect switch 1300and the attached network equipment 1302 to carry or transport the lightpulses or photon pulses of the data signals there-between. That is, theattached network equipment 1302 is coupled or attached to the opticalcross-connect switch 1300 to accept data signals transported over theone or more data lines 1306A-1306N. Data signals from the attachednetwork equipment (ANE) 1302 on the data lines 1306A-1306N are coupledinto the optical cross-connect switch 1300. The optical cross-connectswitch 1300 is coupled or attached to the attached network equipment1302 to accept data signals transported over the one or more data lines1306A-1306N.

The optical cross-connect switch 1300 includes the network managementcontroller (NMC) 1310 (also previously referred to herein as a networkcontrol module (NCM)), one or more I/O port cards 1314A-1314N and1315A-1315N, and the optical switch fabric 1312. The optical switchfabric generates optical paths therein in order to cross-connect (alsoreferred to as route or switch) optical signals from an I/O port card onthe input side to an I/O port card on the output side. The optical pathsare bi-directional in that the optical signal can flow in eitherdirection with the optical path coupled to either an input port or anoutput port of a port card. I/O port cards can also be referred to asline cards, port cards, or I/O port modules as previously used herein.Each of the one or more I/O port cards 1314A-1314N and 1315A-1315N ofthe optical cross-connect switch 1300 includes an optical input port andan optical output port to couple to the optical fibers of the fullduplex data lines 1306A-1306N. Port cards 1314 can also include somesimple monitoring functions by tapping off a small percentage of theenergy of the optical signal and converting it into an electrical signalusing an inexpensive O/E. However, port cards 1314 do not need afull-fledged receiver for extensive monitoring of parameters such as abit error rate or the presence of a particular frame because thesignaling interface of the present invention is provided in order toacquire such information from other network equipment.

The attached network equipment 1302 includes a network managementcontroller 1320 and one or more I/O port cards 1321A-1321N (alsoreferred to as line cards or herein previously as I/O port modules).Each of the one or more I/O port cards 1321A-1321N includes anoptical—electrical-optical converter 1322A-1322N on its data input portsto couple to optical fibers of the data lines 1306A-1306N. The one ormore optical—electrical-optical converters 1322A-1322N first convert theoptical signals on the data lines 1306A-1306N into electrical signalsand then convert the electrical signals into optical signals.

The one or more optical—electrical-optical converters 1322A-1322N can beused for a number of reasons including to generate electrical signals tomonitor the optical signal as well as to amplify (i.e. regenerate) lowlevel incoming optical signals. In the conversion process, the one ormore optical—electrical-optical converters 1322A-1322N provideinformation regarding the optical signals in electrical form which istapped for monitoring purposes as the electrical signals 1323A-1323N.The electrical signals 1323A-1323N may include information from othersources of the respective port card 1315A-1315N that may be of relevanceto the optical cross-connect switch. The one or moreoptical—electrical-optical converters 1322A-1322N and their electricalsignals were originally used in the attached network equipment 1302 tofacilitate its functionality and monitor its performance and not providefeedback to an optical cross-connect switch.

The electrical signals 1323A-1323N are coupled into the networkmanagement controller (NMC) 1320 of the attached network equipment 1302.In one embodiment, the electrical signals 1323A-1323N, or arepresentation thereof, are signaled back to the optical cross-connectswitch 1300 over the out-of-band signaling channel on the network 1304.The electrical signals 1323A-1323N, or a representation thereof, aretransmitted from the network management controller 1320 in the attachednetwork equipment 1302 to the network management controller 1310 in theoptical cross-connect switch 1300. In this manner, the attached networkequipment 1302 signals to the optical cross-connect switch 1300. In asimilar manner with differing information, the optical cross-connectswitch 1300 can signal to the attached network equipment 1302 over theout-of-band signaling channel.

The optical—electrical-optical converters 1322A-1322N are expensive andas a result of being already available in the attached network equipment1302, they are not needed in the optical cross-connect switch 1300 ifthe signaling interface of the present invention is provided. This canprovide considerable cost savings when purchasing optical cross-connectswitches 1300.

In FIG. 13, the attached network equipment 1302 that is coupled to theoptical cross-connect switch 1300 is a WDM line terminal 1302 which alsoincludes a wave division multiplexer/demultiplexer 1324 along with thenetwork management controller 1320 and the one or more port cards1321A-1321N with the optical—electrical-optical converters 1322A-1322N.The wave division multiplexer/demultiplexer 1324 couples to a pair ofoptical fibers on one end to carry wave divisioned multiplexed signals1326 in each direction for full duplex communication and one or morepairs of optical fibers on an opposite end to couple to the I/O portcards 1321A-1321N. The wave division multiplexer/demultiplexer 1324multiplexes multiple light signals received from respective opticalfibers in one direction into a wave division multiplexed signal 1326having multiple light signals of different wavelengths carried over oneoptical fiber, The wave division multiplexer/demultiplexer 1324demultiplexes a wave division multiplexed signal 1326 in an oppositedirection having multiple light signals of different wavelengths carriedover one optical fiber into multiple light signals for transmission tothe optical cross-connect switch 1300 over the data lines 1306A-1306N.The wave division multiplexed signal 1326 provides greater databandwidth and channel capacity over an optical fiber.

The network connection to the network 1304 for the out-of-band signalingchannel is an Ethernet, an RS232 or other similar connection connectingtogether the network management controllers (NMCs) (also previouslyreferred to as a network control module (NCM)) of the opticalcross-connect switch 1300 and the attached network equipment 1302.Because the out-of-band signaling channel is provided over the network1304, other network equipment or monitoring stations can receiveinformation and transmit information or control signals over the out-ofband signaling channel regarding the network, the network equipment andthe optical network components connected to the network. Thus,management of the network can be facilitated regarding the opticalcross-connect 1300, the attached network equipment 1302, and othernetwork equipment using the out-of-band signaling channel. Theout-of-band signaling channel over the network can be considered acentralized signaling interface.

Referring now to FIG. 14 a block diagram of a decentralized signalinginterface between an optical cross-connect switch 1400 and attachednetwork equipment 1402 is illustrated. The decentralized signalinginterface is provided by one or more dedicated signal lines 1404A-1404Nbetween the optical cross-connect switch 1400 and the attached networkequipment 1402. The one or more dedicated signal lines 1404A-1404N canbe formed by using low-cost multimode (MM) optical fibers or by usinglow cost electrical wire links.

The one or more dedicated signal lines 1404A-1404N replaces theout-of-band signaling channel of the network 1304. Whereas theout-of-band signaling channel of the network 1304 provided signalsregarding switching each of the optical signals on multiplecommunication channels, one dedicated signal line 1404 providesinformation regarding switching of optical signals on one communicationchannel. Furthermore, the centralized signaling between the between theoptical cross-connect switch 1400 and the attached network equipment1402 was performed by the centralized NMCs 1310 and 1320 at a centralcontrol level. In contrast, decentralized signaling is performed by theI/O port cards (also referred to as line cards or herein previously asI/O port modules) at a line-card level which is a much lower level thanthe centralized NMC level.

In the embodiment illustrated in FIG. 14, the optical cross-connectswitch 1400 includes the network management controller (NMC) 1310, oneor more I/O port cards 1414A-1414N (also referred to as line cards, portcards and I/O port modules), and the optical switch fabric 1312. Each ofthe one or more I/O port cards 1414A-1414N and 1415A-1415N of theoptical cross-connect switch 1400 includes an optical input port and anoptical output port. Each of the one or more port cards 1414A-1414Nfurther may include optical-electrical converters (O/E) 1416A-1416N ifthe dedicated signal line is an optical fiber. The optical-electricalconverters 1416A-1416N of the optical cross-connect switch are much lessexpensive than optical-electrical-optical converters (O/E/O) that mightotherwise be needed therein. Optical-electrical converters (O/E) aretypically a fiber optic receiver module which includes a photodetector.

The attached network equipment 1402 includes one or more port cards1421A-1421N (also referred to as line cards). Each of the one or moreport cards 1321A-1321N includes an optical—electrical-optical converter1322A-1322N on its data input ports to couple to optical fibers of thedata lines 1306A-1306N. In the case the dedicated signal lines1404A-1404N are optical fibers, each of the one or more port cards1321A-1321N further includes an electrical-optical converter (E/O)1422A-1422N to convert electrical signals 1423A-1423N into opticalsignals. Electrical-optical converters (E/O) are typically a fiber optictransmitter module which include a semiconductor laser with controlelectronics. Optical-electrical-optical converters (O/E/O) are typicallya combination of an O/E converter coupled together with an E/Oconverter.

The attached network equipment 1402 that is illustrated coupled to theoptical cross-connect switch 1400 is a WDM line terminal 1402. A WDMline terminal 1402 also includes a wave division multiplexer 1324 alongwith the one or more port cards 1421A-1421N with theoptical-electrical-optical converters 1322A-1322N.

The one or more optical—electrical-optical converters 1322A-1322N firstconvert the optical signals on the data lines 1306A-1306N intoelectrical signals and then convert the electrical signals into opticalsignals. The one or more optical—electrical-optical converters1322A-1322N are tapped to provide information regarding the opticalsignals in electrical form on the electrical signals 1323A-1323N. Theport cards 1421A-1421N of the attached network equipment 1402 detectother relevant information and communicate it directly to the respectiveport cards 1414A-1414N of the optical cross-connect switch 1400 over thededicated signal lines 1404A-1404N rather than signaling between thecentral NMCs 1310 and 1320. Similarly, port cards 1414A-1414N of theoptical cross-connect switch 1400 can detect relevant information andcommunicate it directly to the respective port cards 1421A-1421N of theattached network equipment 1402 over the dedicated signal lines1404A-1404N.

Having established a signaling interface, it can be used for severalpurposes. The signaling interface can be used to enable fast networkrestoration through the optical cross-connect switch (OXC) in the eventof network failures. Network failures include signal failures such as aloss of signal (LOS) or signal degradation such as through a bit errorrate (BER) or other commonly know optical failure mechanisms. Attachednetwork equipment (ANE) can detect failures in real time by using itsO/E/Os and convey this information to the optical cross-connect switchover the signaling interface so that it can perform network restoration.The optical cross-connect switch is typically without O/E/Os and may notbe able to detect the failure due to the otherwise relatively simplemonitoring usually found within an optical cross-connect switch.

Another use for the signaling interface is to allow attached networkequipment (ANE) to control the optical cross-connect switch (OXC). Forexample, the attached network equipment (ANE) could signal to the OXCover the signaling interface in order for it to provide a particularswitch configuration.

Another use for the signaling interface is so that the opticalcross-connect switch can signal to the attached network equipment to setspecific parameters therein. For example during setting up a connection,the optical cross-connect switch may ask the attached equipment toadjust its transmitter power level.

Another use for the signaling interface is to allow attached networkequipment (ANE) to request a connection through the opticalcross-connect switch (OXC). The optical cross-connect switch (OXC) setsup the connection and informs the attached network equipment (ANE) whenits available.

Another use for the signaling interface is to perform protectionswitching between the OXC and the attached network equipment. Forexample, the signaling interface could be provided by one spare fiberfacility for N working facilities between the attached equipment and theOXC. If one of these N facilities fails, the signaling channel is usedby both devices to switch connections from the failed facility to thespare facility.

VI. Optical to Electrical to Optical Conversion

Specific configurations for building optical cross-connect switchingsystems are disclosed herein. Optical-to-electrical-to-opticalconverters (O/E/Os) are included on input and output ports to an opticalswitch fabric, a core element of an optical cross-connect. Methods forperforming bridging, test access, and supporting redundant cores arealso disclosed.

Referring now to FIG. 15, a block diagram of an optical cross-connectswitch (OXC) 1500 is illustrated. An optical cross-connect switch isalso referred to herein as an optical cross-connect, an OXC, and anoptical cross-connect switching system. The optical cross-connect switch(OXC) 1500 includes an optical switch fabric 1510 (also referred to asthe optical switch core) and various I/O port cards. The opticalcross-connect switch 1500 has one or more optical input ports1501A-1501N and one or more optical output ports 1502A-1502N provided byvarious I/O port cards which are also referred to herein as I/O portmodules or simply port cards. The various I/O port cards can include oneor more smart port cards 1504A-1504L and 1504A′-1504M′ (generallyreferred to as smart port cards 1504) and/or one or more passive portcards 1503A-1503N (generally referred to as passive port cards 1503).The optical switch fabric 1510 in one embodiment is an N×N opticalswitch core having N inputs and N outputs. The optical switch fabricgenerates optical paths therein in order to cross-connect (also referredto as route or switch) optical signals from an input side to an outputside. The optical paths are bi-directional in that the optical signalcan flow in either direction with the optical path coupled to either aninput port or an output port of a port card. Each input and output portand each input and output of the optical switch core is respectivelyassociated with an input and output path of one of the one or more portcards 1504 and 1503. The input path and the output path are paths overwhich the optical signals propagate in the port card relative to theoptical switch fabric 1510.

The port cards 1504 and 1503 can be classified as either passive portcards or as smart port cards. The one or more smart port cards includeoptical-electrical-optical converters (O/E/O) 1507 in an optical inputpath, an optical output path, or both their optical input and outputpaths. Optical-electrical-optical converters are also referred to hereinas optical-to-electrical-to optical converters. The O/E/Os 1507 areprovided in an optical cross-connect switch for several reasons. TheO/E/Os provide a standardized interface with other equipment; enable anoptical cross-connect switch to perform detailed real-time performancemonitoring, such as bit error rates, and to determine failures in thenetwork using this monitoring; can isolate one segment of the networkfrom another segment; and can provide wavelength conversion. The one ormore passive port cards 1503 do not have an optical-electrical-opticalconverter (O/E/O) 1507 to provide optical-electrical-optical conversionin either of their optical input paths 1513 or optical output paths1514.

The smart port cards 1504A-1504M have an O/E/O 1507 in their opticalinput paths 1511 and not their optical output paths 1512. The O/E/O 1507in the optical input paths 1511 is also referred to being on the inputside of the optical cross-connect switch 1500. Locating an O/E/O on theinput isolates the optical losses associated with an opticalcross-connect switch from the input optical signal. Additionally, anO/E/O on the input side can regenerate an input optical signal andprovide a stronger optical signal for propagation through a switchfabric of an optical cross-connect switch. An O/E/O on the input side ofan optical cross-connect switch (OXC) can also provide wavelengthconversion and/or translation before the signal is routed through theswitch fabric of the optical cross-connect switch. That is, the O/E(optical receiver) of the O/E/O can accept a full range of photonfrequencies and convert it into an electrical signal while the E/Oconversion may be provided by a multimode laser for example that can betuned to a desired photon wavelength (i.e. frequency) output to providewavelength conversion. Otherwise, the E/O conversion may be provided bya single mode laser for example which has the desired photon wavelengthoutput as opposed to be tunable. Additionally, the O/E/O on the inputside can generate an electrical signal representing the incoming opticalsignals for monitoring purposes. A processor can process the electricalform of the incoming optical signals in a binary coded form to makecontrol decisions as well as pass performance information to othernetwork equipment regarding the input optical signals input. Forexample, the electrical signal may indicate the lack of an opticalsignal or errors in an optical signal.

The smart port cards 1504A′-1504L′ have an O/E/O 1507 in their opticaloutput paths 1512 and not their optical input paths 1511. The O/E/O 1507in the optical output paths 1512 is also referred to as being on theoutput side of the optical cross-connect switch 1500. Locating an O/E/Oon the output path isolates the optical cross-connect switch from thenetwork to which it is attached. For example negative optical conditionsor negative timing parameters may exist on the cross connected signaloutput from the switch fabric, such as low optical power, wrongwavelength, poor spectral quality, overpower, etc. The O/E/O within theoutput path can isolate these conditions from the optical network.Additionally, an O/E/O on the output side can regenerate an the opticalsignal output from the switch fabric and provide a stronger opticalsignal at the output of an optical cross-connect switch. An O/E/O on theoutput side of an optical cross-connect switch (OXC) can also providewavelength conversion and/or translation after the signal has beenrouted through the switch fabric of the optical cross-connect switch.The optical signals that are input into the optical cross-connect switchmay have a wide range of wavelengths and the O/E/O can convert them intoone or more desired wavelengths as the output optical signal.Additionally, the O/E/O on the output side can generate an electricalsignal representing the outgoing optical signals from the opticalcross-connect switch. A processor can process the electrical form of theoutgoing optical signals in a binary coded form to make controldecisions as well as pass performance information to other networkequipment regarding the output optical signals. For example, theelectrical signal may indicate the lack of an optical signal and afailure in the optical cross-connect switch or errors in an opticalsignal.

In any case, the smart port cards 1504 converts the optical signal inthe optical path into an electrical form, process the electrical signalif desired, generate a desired optical signal from the electricalsignal, and retransmit the optical signal over the respective opticalinput or output path in optical form.

An optical—electrical-optical converter 1507 first converts an inputoptical signal into an electrical signal. The electrical signal can betapped out to provide information regarding the input optical signalinput into the O/E/O 1507. the O/E/O 1507 then converts the electricalsignal into an output optical signal. The output optical signal from theO/E/O is similar to the input optical signal into the O/E/O in that thesame data is being carried but the optical signal amplitude may beamplified, wavelength converted or otherwise improved in some way overthat of the input optical signal. The O/E/O 1507 provides the conversionwith little delay in the data carried by the optical signal.

While an O/E/O 1507 may be in both the optical input path of a smartport card (input side of OXC) and the output path of a smart port card(output side of OXC), it is required only in one of the optical paths ofone port card for the more sophisticated applications of the opticalcross-connect switches. Smart port cards 1504 in FIG. 15 of the opticalcross-connect switch 1500 illustrate this principle. For example, anoptical path 1515A in the optical switch fabric 1510 couples the opticalinput path 1511 of the smart port card 1504A with the optical outputpath 1514 in the passive port card 1503A. The optical signal isregenerated by the O/E/O 1507 in the optical input path 1511 of thesmart port card 1504A. As another example, an optical path 1515B in theoptical switch fabric 1510 couples the optical input path 1511 of thesmart port card 1504B to the optical output path 1512 of the smart portcard 1504N. In this example, the optical signals are monitored by theO/E/O 1507 in the optical output path 1512 of the smart port card 1504N.As yet another example, an optical path 1515C in the optical switchfabric 1510 couples the optical input path 1513 of the passive port card1503A with the optical output path 1512 of the smart port card 1504B. Inthis example, the optical signals are regenerated by the O/E/O 1507 inthe optical output path 1512 of the smart port card 1504B. Because theO/E/O 1507 is rather expensive, using only one O/E/O 1507 in a smartport card 1504 saves significant costs.

The type of port card to use, smart or passive, depends on theapplication of the optical cross-connect 1500 in the communicationnetwork. For a simple provisioning application where the opticalcross-connect switch 1500 is used to set up optical connections, passiveport cards 1503 need only be utilized. For a more sophisticatedapplication where full-featured performance, fault management andoptical protection are desired, smart port cards 1504 are needed. Notethat a mixture can be used where some of the port cards in the opticalcross-connect 1500 are passive port cards 1503 and others are smart portcards 1504 such as that illustrated in FIG. 15.

Referring now to FIG. 16, a block diagram of an optical cross-connectswitch 1600 having a one and two tiered port card arrangement isillustrated. The optical cross-connect 1600 has one or more opticalinput ports 1601A-1601Z and one or more optical output ports 1602A-1602Zprovided by the various port cards. In the two tiered port cardarrangement of the optical cross-connect 1600, one or more smart portcards 1604A-1604M and 1604A′-1604N′ (generally referred to as 1604) arecoupled to one or more passive port cards 1603A-1603N (generallyreferred to as 1603) to access the optical switch fabric 1610 (alsoreferred to as an optical switch core). That is, the optical input pathsof the smart port cards are coupled to the optical input paths of thepassive port cards and the optical output paths of the passive portcards are coupled to the optical output paths of the smart port cards.Thus, input optical signals on the optical input paths of the smart portcards are coupled into the optical input paths of the passive portcards. Output optical signals on the optical output paths of the passiveport cards are coupled into the optical output paths of the smart portcards in the two tiered port card arrangement. Note that an opticalsignal may or may not need to be passed through a smart port card beforebeing passed through a passive port card. The passive port card 1603Zillustrates this case. Thus, passive port cards alone as a single tieredport card arrangement can be intermixed within the two tiered port cardarrangements.

In either the single or two tiered port card arrangement in the opticalcross-connect switch 1600, only the passive port cards 1603A-1603Z areused to access the optical switch fabric 1610. The optical signals onthe optical input path 1613 and the optical output path 1614 of thepassive port card 1603Z need to couple to an optical output path 1612and an optical input path 1611 respectively each having an O/E/O 1507 inorder to regenerate the optical signals. Exemplary switching of opticalsignals is illustrated in FIG. 16 by the optical paths 1615A-1615E inthe optical switch fabric 1610. Unidirectional and bi-directionalconnections can be made through the optical cross-connect switch betweenI/O port cards. Bi-directional connections are more typically the case.The optical paths 1615A, 1615B and 1615E illustrate exemplary opticalpaths (also referred to as light paths) through the optical switchfabric 1610 for unidirectional connections between I/O port cards. Theoptical paths 1615C and 1615D illustrate exemplary optical paths throughthe optical switch fabric 1610 for bi-directional connections betweenI/O port cards. The settings of the optical switch fabric 1610 change inorder to rearrange the optical paths between the I/O port cards asdesired.

The passive port cards 1603A-1603Z in the optical cross-connect 1600provide control of the optical signals into and out of the opticalswitch fabric 1610. The smart port cards 1602A-1602M having the O/E/Os1507 provide regeneration, performance monitoring, fault management andprotection switching functions. By splitting the functionality of theport cards in this manner into the two tiered arrangement, replacementof faulty port cards can be less costly. The two tiered arrangement ofI/O port cards also allows a system to be deployed with passive portcards initially with smart port cards being added later as needed. Alsothe smart port cards typically have different power and coolingrequirements than the passive port cards, and may be located in separateshelves to provide additional cooling.

In addition to basic switching functions provided by an opticalcross-connect, it is desirable to provide bridging, test access andsupport for redundant optical switch fabrics (also referred to asredundant optical switch cores).

Referring now to FIG. 17, a block diagram of an optical cross-connect1700 is illustrated. The optical cross-connect 1700 has one or moreoptical input ports 1701A-1701N and one or more optical output ports1702A-1702N provided by the various port cards. The opticalcross-connect 1700 includes smart port cards 1704A-1704N and1704A′-1704M′ that provide bridging for the optical switch fabric 1710.Bridging means that at least two optical paths are provided between portcards carrying the same optical signals. The optical switch fabric 1710illustrates exemplary optical signal paths 1715A-1715D and redundantoptical signal paths 1715A′-1715D′. If one optical path fails in theoptical switch fabric 1710, the redundant optical path in the opticalswitch fabric 1710 continues to handle the data carried by the opticalsignals. For example, if the optical path 1715A fails in the opticalswitch fabric 1710, the optical path 1715A′ continues to carry theoptical signals. The redundant optical path 1715A′ can be thought asbridging a gap in the optical path 1715A when it fails.

An optical path or the generation of optical signals in an optical pathcan fail terminating the optical signal completely or generating biterrors at a high rate over that of the other optical signal or opticalpath. By monitoring the optical signal inputs and/or outputs from theoptical network equipment such as the optical cross-connect switch, adetermination can be made whether to switch from one optical signal inone optical path to another. The optical path and or optical signal inthe optical path can fail for a variety of reasons including one or morefaulty components or a failure in control.

To generate a redundant optical path in the optical cross-connect switch1700, an input optical signal is input into an input port such as inputport 1701A. In one type of smart port card, illustrated by smart portcards 1704A-1704N (generally referred to as 1704), the input opticalsignal is coupled into an O/E/O 1707 in the input path 1711. The O/E/O1701 converts the optical signal into an electrical signal which is thenconverted back into an optical signal. The electrical signal is used tomonitor the input optical signals. The O/E/O 1707 is coupled to anoptical splitter 1708 to split the incoming optical signal into at leasttwo optical signals on at least two split optical paths 1721A and 1722A.The splitter 1708 can be used to split the incoming optical signal intomore than two split optical paths to provide greater redundancy andreliability if desired but is typically not needed. The optical splitter1708 in one embodiment is a passive optical coupler. While the datasignal or pulses of light of the split optical signals are the same, theenergy level of the incoming optical signal can be split equally orunequally into the at least two optical signals on the at least twosplit optical paths 1721A and 1722A. The at least two split opticalpaths are coupled into the optical switch fabric 1710 and switched toanother port card respectively over the optical paths 1715A and 1715A′for example. The redundant optical signals in the optical paths 1715Aand 1715A′ are coupled into a switch 1709 of the smart card 1704B forexample over the split paths 1723B and 1724B respectively. The switch1709 is an optical switch. As its output, the switch 1709 selectsbetween the at least two optical signals in the at least two splitoptical paths 1715A and 1715A′. The selected output of the opticalswitch 1709 is coupled into the optical output path 1712 of the smartport card and the output port 1702B of the optical cross-connect switch1700. In the case that one of the two optical signals in the at leasttwo split optical paths fails or has errors, the optical switch 1709 canselect the alternate optical path as its output to overcome the pathfailure or the errors.

In another type of smart port card, illustrated by smart port cards1704A′-1704M′ (generally referred to as 1704′), an input optical signalat the input port is first coupled into a splitter 1708′ in the opticalinput path 1711. The incoming optical signal is first split by thesplitter 1708′ into at least two optical signals on at least two splitoptical paths 1721C and 1722C for example. The at least two opticalsignals on the at least two split optical paths 1721C and 1722C are thencoupled into the optical switch fabric 1710 for switching. In theoptical switch fabric 1710, the split optical signals are routed overdifferent optical paths such as optical paths 1715C and 1715C′. Thesplit optical signals on the different optical paths are coupled intothe same switch of a port card such as switch 1709′ of the smart portcard 1704M′ via the optical paths 1723M and 1724M for example. Theswitch 1709′ is an optical switch. As its output, the switch 1709′selects between the at least two optical signals in the at least twosplit optical paths 1715C and 1715C′ for example. The selected output ofthe optical switch 1709′ is coupled into the optical output path 1712 ofthe smart port card and the output port 1702M of the opticalcross-connect switch 1700. In the case that one of the two opticalsignals in the at least two split optical paths fails or has errors, theoptical switch 1709′ can select the alternate optical path as its outputto overcome the path failure or the errors. The output of the opticalswitch is coupled into the O/E/O 1707′ on the smart port card forregenerating the optical signals. With the O/E/O 1707′ in the outputpath, regeneration is performed post split. In this manner, the O/E/Osdo not need to be duplicated in the input path and output path for eachconnection of a communication channel over the optical cross-connectswitch 1700. The monitoring provided by the O/E/Os 1707 and 1707′ in thesmart port cards in the optical cross-connect switch 1700, assist in theselection between the at least two optical signal in the at least twosplit optical paths by the optical switches 1709 and 1709′ respectively.If the monitoring determines that there is no signal at the output ofthe optical switch 1709′ and its known that there should be a signalpresent, the optical switch 1709′ can select the alternate path. If themonitoring determines that there is an input optical signal into thesplitter 1708 and its known that it should be present at the output of aswitch 1709, the alternate path can be selected.

In either case, the port cards of the optical cross-connect switch 1700of FIG. 17 split the incoming optical signal at an input port into atleast two split optical signals to propagate over two different opticalpaths and provide redundancy in how the data signal is routed over theoptical switch fabric. The port cards then select which of the at leasttwo split optical signals to couple into an output port of the opticalcross-connect.

Referring now to FIG. 18, a block diagram of an optical cross-connectswitch 1800 is illustrated. The optical cross-connect switch 1800 is analternate embodiment to provide bridging over an optical switch fabric1810. The optical cross-connect switch 1800 has one or more opticalinput ports 1801A-1801N and one or more optical output ports 1802A-1802Nprovided by the various port cards.

Using one type of smart port card, the incoming optical signal is firstconverted from an optical signal in the optical domain into anelectrical signal in the electrical domain and fanned out (i.e.electrically split into two equal electrical signals) by coupling intoto two optical transmitters (i.e. an electrical to optical convertersuch as a semiconductor laser). The two optical transmitters convert inparallel the electrical signal into two optical signals in the opticaldomain. The two optical signals generated by the two opticaltransmitters (electrical-optical converters) are substantially similar.The two optical signals are then routed through the optical switchfabric through differing optical paths. A selection is then made at theoutput of the optical switch fabric between the two optical signals inorder to generate the output optical signal from the opticalcross-connect. If one path of the two optical signals should fail, theopposite path is selected.

Using another type of smart port card, the incoming optical signal isoptically split into two split optical signals which are routed over theoptical switch fabric. At the output of the optical switch fabric, thetwo split optical signals in the optical domain are coupled into twooptical receivers (each an optical to electrical converter (O/E) such asa photodiode) to convert them into two electrical signals respectivelyin the electrical domain. The two electrical signals are then coupledinto multiplexer to electronically select which one of the two should betransmitted out the output port of the optical cross-connect by anoptical transmitter (i.e. an electrical to optical converter such as asemiconductor laser). The optical transmitter converts the selectedelectrical signal in the electrical domain into an optical signal in theoptical domain.

Referring to FIG. 18, the optical cross-connect switch 1800 can includeone or more smart port cards 1804A-1804N and/or one or more smart portcards 1804A′-1804M′. In either case, the smart port cards provide twodifferent optical paths through the optical switch fabric 1801 for thesame communication channel connection. For example, optical paths1815A-1815D are one path for the communication channels while opticalpaths 1815A′-1815D′ are another both carrying the same data signals. Ifone optical path should fail generating a gap in the connection, theother path is selected to bridge the gap and to allow a continuous flowof data for the given communication channel connection. Bridging in thismanner increases the reliability of the optical cross-connect.

The smart port cards 1804A-1804N include an optical receiver 1817 (i.e.an optical to electrical converter (O/E) such as a photodiode) which iscoupled to a pair of optical transmitters 1818A and 1818B (i.e. anelectrical to optical converter (E/O) such as a semiconductor laser) inthe input path 1811. Thus, in the input path 1811 of the smart portcards 1804A-1804N an optical-electrical-optical conversion (O/E/O) isperformed. In the output path 1812, the smart port cards 1804A-1804Ninclude an optical switch 1809 to select between two optical signals.The optical transmitters 1818A and 1818B generate the two paralleloptical signals that are routed over two paths in the optical switchfabric such as optical paths 1815A and 1815A′. The optical switch 1809selects between the two parallel optical signals to generate one as theoutput of the optical cross-connect 1800 on an output port. If theselected path should fail, the optical cross-connect switches to theother optical signal carried over the other optical signal path.

The smart port cards 1804A′-1804M′ include an optical splitter 1808 inthe input path 1811 to split the incoming optical signal into two splitoptical signals. The two split optical signals are coupled into theoptical switch fabric 1810 to be routed over two separate optical paths.For example, the smart port card 1804A′ would couple a split incomingoptical signal into the optical paths 1815C and 1815C′ of the opticalswitch fabric. In the output path 1812, the smart port cards1804A′-1804M′ include a pair of optical receivers 1828A and 1828B, amultiplexer 1829, and an optical transmitter 1827. The pair of opticalreceivers 1828A and 1828B (i.e. an optical to electrical converter (O/E)such as a photo-diode) receive the split optical signals routed over thetwo separate optical paths. A benefit of locating these receivers afterthe switch fabric(s) is that they can accept a full range of wavelengthsof photons due to dense wave-length division multiplexed (DWDM) opticalsignals. The wide range of wavelengths of optical signals over theoptical paths in the optical cross-connect can exist due to DWDM. Beingable to cross-connect any optical signal to the O/E/O over a range ofwavelengths is desirable to provide wavelength conversion/translation inthe optical cross-connect switch. Another benefit is that if somenegative optical conditions or negative timing parameters exist in thecross connected optical signal from the switch fabric, such as lowoptical power, wrong wavelength, poor spectral quality, overpower, etc.within the cross-connect switch, it can be isolated by the O/E/O beforebeing output to the network. The split optical signals are convertedinto two electrical signals by the optical receivers 1828A and 1828B andcoupled into the multiplexer 1829. The two electrical signals can alsobe monitored locally to determine which should be selected to generatethe optical output signal. It can also be forced to switch by means ofexternal communication control, if external monitoring methods areemployed. The multiplexer 1829 electronically selects one of the twoelectrical signals to be coupled into the optical transmitter 1827 (anelectrical to optical converter (E/O) such as a semiconductor laser). Ifthe two signals being selected from have the same data and protocol, asexpected, it is envisioned that the monitored switching between the twowithin the multiplexer could be hitless, i.e. produce no errors on theselected electrical signal. This behavior is very beneficial to bridgeand roll applications and those that have Forward-Error-Correction dataencoding schemes. This would also apply to SONET and SONET like datastreams as well as those employing a ‘wave wrapper’ protocol. Theoptical transmitter 1827 converts the selected electrical signal in theelectrical domain into an optical signal in the optical domain fortransmission out over the output port of the optical cross-connect 1800.Thus, in the output path 1812 of the smart port cards 1804A′-1804M′ anoptical-electrical-optical conversion (O/E/O) is performed.

Bridging in this manner provides that if a path or a component in thepath fails, the other path and components can handle the data flow overthe communication channel in the optical cross-connect. A disadvantageto the bridging provided by the optical cross-connects 1700 and 1800 isthat fewer communication channels can be supported because of theredundant optical paths formed in the optical switch fabrics 1710 and1810 respectively. One way to alleviate this problem is to use aredundant optical switch fabric to provide the redundant path.

Referring now to FIGS. 19A-19G, block diagrams of embodiments of opticalcross-connect switches 1900A-1900G are illustrated. The opticalcross-connect switches 1900A-1900G include port cards that providebridging by using two or dual optical switch fabrics (also referred toas optical switch cores). The incoming signal is split into at least twosignals with one portion being coupled into one optical switch fabricwith another portion of the signal being coupled into the other opticalswitch fabric. While one acts as an active optical switch fabric, theother acts as a redundant optical switch fabric, for each path throughthe system. Providing a redundant optical switch fabric also providesreliability in case there is a problem in control of one of the opticalswitch fabrics, Furthermore, the redundant optical switch fabricprovides hot swapability in that while one is having its optical switchfabric or other control systems updated or replaced, the other cancontinue to provide optical switching. The optical cross-connectswitches 1900A-1900G also includes a test access/monitor port card totest and monitor the optical paths through the two optical switchfabrics to determine if there is a failure mechanism or not.

Referring to FIG. 19A, the optical cross-connect 1900A includes a firstoptical switch fabric 1910A and a second optical switch fabric 1910B andhas one or more optical input ports 1901A-1901N and one or more opticaloutput ports 1902A-1902N provided by the various port cards. The opticalcross-connect 1900 also includes one or more smart port cards1904A-1904N (generally referred to as 1904) and/or one or more smartport cards 1904A′-1904M′ (generally referred to as 1904′). The opticalcross-connect 1900 can also include one or more test port/monitor cards1905. The smart port cards 1904A-1904N provide an O/E/O 1907 in theirinput paths while the smart port cards 1904A′-1904M′ provide an O/E/O1907′ in their output paths. The smart port cards 1904A-1904N and1904A′-1904M′ each have an optical splitter 1908 and 1908′ respectivelyin their input paths. The smart port cards 1904A-1904N and 1904A′-1904M′each have an optical switch 1909 and 1909′ respectively in their outputpaths. The O/E/Os 1907 and 1907′, optical switches 1909 and 1909′, andthe optical splitters 1908 and 1908′ are optically coupled togetherwithin the smart port cards 1904A-1904N and 1904A′-1904M′ as shown andillustrated in FIGS. 19A and 19B. In either type of smart port cards1904 or 1904′, the optical splitter 1908 or 1908′ splits the incomingoptical signal into two split optical signals over two different opticalpaths one of which is coupled into the first optical switch fabric 1910Aand the other which is coupled into the second optical switch fabric1910B. In either type of smart port cards 1904 or 1904′, the opticalswitch 1909 and 1909′ selects an optical signal from between two opticalsignals over two differing optical signal paths one of which is receivedfrom the first optical switch fabric 19010A and the other of which isreceived from the second optical switch fabric 1910B. In this mannershould an optical signal path in one of the two switch fabrics fail forany reason, the optical switch 1909 or 1909′ only need select theopposite signal path. For example consider the exemplary optical path1915A in the optical switch fabric 1910A and the optical path 1915A′ inthe optical switch fabric 1910B. Splitter 1908 in the smart port card1904A splits an incoming optical signal into two split optical signalson optical paths 1921A and 1922A. The signal on the optical path 1921Ais coupled into the first optical switch fabric 1910A and the signal onthe optical path 1922A is coupled into the second optical switch fabric1910B. The optical switches 1910A and 1910B switch these optical signalsinto the exemplary optical signal paths 1915A and 1915A′ respectively.The optical signal path 1915A in the optical switch fabric 1910A iscoupled into the optical path 1923N which is coupled into the opticalswitch 1909′ of the smart port card 1904N. The optical signal path1915A′ in the optical switch fabric 1910B is coupled into the opticalpath 1924N which is coupled into the optical switch 1909′ of the smartport card 1904N. In one case, the optical switch 1909′ of the smart portcard 1904N selects the optical signals over the optical path 1915A sothat the first optical switch fabric 1910A is acting as the activeoptical switch fabric. In another case, the optical switch 1909′ of thesmart port card 1904N selects the optical signals over the optical path1915A′ so that the second optical switch fabric 1910B is acting as theactive optical switch fabric. If either optical switch fabric failsgenerating a gap, the other is automatically selected by the smart portcards to bridge the gap.

In this case, optical signals from the smart port card 1904A are coupledinto the smart port card 1904N such that only one O/E/O 1907 is neededto regenerate the optical signals input into the optical cross-connect1900. If it is desirable to regenerate optical signals into as well asout of the optical cross-connect 1900, optical signals from one of thesmart port cards 1904A-1904N can be coupled into one of the smart portcards 1904A′-1094M′ which have an O/E/O 1907′ to regenerate the outputoptical signals in the output path.

Other port cards including passive port cards can be used with more thanone optical switch fabric to provide at least one redundant opticalswitch fabric. FIGS. 19B-19G illustrate exemplary embodiments of othercombinations of port cards that can be used with the two optical switchfabrics 1910A and 1910B.

Referring now to FIG. 19B, the optical cross-connect switch 1900Bincludes smart port cards 1804A-1804N, smart port cards 1804A′-1804M′,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. The elements of smart port cards 1804A-1804N and smart port cards1804A′-1804M′ were previously discussed with reference to FIG. 18. Theoptical cross-connect switch 1900B provides redundancy similar to theoptical cross-connect switch 1900A but uses differing port cards havingdifferent components.

Referring now to FIG. 19C, the optical cross-connect switch 1900Cincludes smart port cards 1944A-1944N, smart port cards 1944A′-1944M′,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. Smart port cards 1944A-1944N and smart port cards 1944A′-1944M′utilize optical switches 1928 and 1928′ as opposed to splitters 1908 and1908′ in smart port cards 1904A-1904N and 1904A-1904M′ respectivelywhich were previously described. Optical switches 1928 and 1928′ provideless optical power loss than the splitters 1908 and 1908′ so that astronger optical signal can be routed through the optical switch fabric.

Referring now to FIG. 19D, the optical cross-connect switch 1900Dincludes smart port cards 1954A-1954N, smart port cards 1954A′-1954M′,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. Smart port cards 1954A-1954N and smart port cards 1954A′-1954M′utilize optical switches 1928 and 1928′ and optical couplers 1929 and1929′ as opposed to splitters 1908 and 1908′ and optical switches 1909and 1909′ in smart port cards 1904A-1904N and 1904A-1904M′ respectivelywhich were previously described. Optical switches 1928 and 1928′ provideless optical power loss than the splitters 1908 and 1908′. Opticalcouplers 1929 and 1929′ act similar to a multiplexer and can be passiveso that no switching control is required.

Referring now to FIG. 19E, the optical cross-connect switch 1900Eincludes smart port cards 1954A-1954M, passive port cards 1953A-1953N,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. Smart port cards 1954A-1954M utilize optical switches 1928 andoptical couplers 1929 as opposed to splitters 1908 and optical switches1909 in smart port cards 1904A-1904N respectively which were previouslydescribed. Each of the passive port cards 1953A-1953N include theoptical switch 1928 in the input path and the optical coupler 1929 inthe output path as shown. Each of the passive port cards 1953A-1953N donot have an O/E/O in either their input path or their output path. Thatis, optical cross connect switches providing at least one redundantoptical switch fabric can also use passive port cards to reduce thenumber of O/E/Os and lower costs.

Referring now to FIG. 19F, alternate combinations of passive port cardsand smart port cards can be combined within optical cross connectswitches having at least one redundant optical switch fabric. In FIG.19F, the optical cross-connect switch 1900F includes smart port cards1904A′-1904M′, passive port cards 1963A-1963N, test port/monitor card1905, network management controller (NMC) 1906, first optical switchfabric 1910A, and second optical switch fabric 1910B. Smart port cards1904A′-1904M′ were previously described with respect to FIG. 19A. Eachof the passive port cards 1963A-1963N include an optical splitter 1968in the input path and an optical switch 1969 in the output path asshown. Each of the passive port cards 1963A-1963N do not have an O/E/Oin either their input path or their output path.

Referring now to FIG. 19G, another embodiment of combinations of passiveport cards and smart port cards is illustrated for an opticalcross-connect switch having a redundant optical switch fabric. In FIG.19G, the optical cross-connect switch 1900G includes smart port cards1904A′-1904M′, one or more passive port cards 1963, one or more passiveport cards 1503, test port/monitor card 1905, network managementcontroller (NMC) 1906, first optical switch fabric 1910A, and secondoptical switch fabric 19101B. Smart port cards 1904A′-1904M′ werepreviously described with respect to FIG. 19A. Each of the one or morepassive port cards 1963 include an optical splitter 1968 in the inputpath and an optical switch 1969 in the output path as shown, Each of theone or more passive port cards 1503 provides only a flow through opticalpath between input and output ports and the optical switch fabrics. Eachof the passive port cards 1963 and 1503 do not have an O/E/O in eithertheir input path or their output path.

While its obvious that other combinations of passive port cards, smartport cards, and optical switch fabrics can be formed, it is desirable toprovide optical signal regeneration by routing an optical signal over anoptical path through the optical cross-connect switch so that at leastone optical-electrical-optical conversion occurs to the optical signalto increase the optical power level at the output from what was receivedat the input. The optical-electrical-optical conversion may used forother reasons as well which were previously described. If it isdesirable, a signaling channel previously described between the opticalcross connect switch and attached network or client equipment can beused to provide information regarding signal conditions and performanceof and around the optical cross-connect switch. The signaling channel isparticularly desirable if nothing but passive port cards without O/E/Osare used in channels of the optical cross-connect switch.

VII. Testing

The optical cross-connect 1900 having redundant optical switch fabricscan readily provide self testability. The optical cross-connect 1900 canoptionally include a test port/monitor card 1905 in order to test theoptical paths through the first and second optical switch fabrics 1910Aand 1910B to perform sophisticated performance monitoring and attachtest equipment if needed. One port of either optical switch fabric canbe dedicated as a test access port. A test port/monitor card is insertedinto the dedicated test access port. The test port/monitor card 1905monitors one of the split signals to determine if there is a failure inthe optical path or not as well as to determine performance measures forthe optical signal including a bit error rate (BER). Any incomingoptical signal passing through the optical cross-connect 1900 can beaccessed and monitored by switching one of the split signals over to thetest access port where the test port/monitor card 1905 is present. Theother part of the split signal continues to be routed through theoptical cross-connect 1900 unaffected. The test access port and testport/monitor card 1905 allow non-intrusive monitoring of the incomingoptical signals.

The test port/monitor card 1905 includes an optical switch 1919 and anoptical to electrical converter (O/E) 1917. The O/E 1917 couples to acontroller within the optical cross-connect 1900 such as the NMC 1906 toprocess the electrical signals from the test port/monitor card 1905representing the optical signal of the tested optical path. The opticalswitch 1917 selects between monitoring an optical path of the firstoptical switch fabric 1910A and an optical path of the second opticalswitch fabric 1910B. The optical switch fabric which is being monitoredcan be referred to as the redundant optical switch fabric, while theoptical switch fabric that is being used to carry data over thecommunication channel connection is referred to as the active opticalswitch fabric. In FIG. 19A, the second optical switch fabric 1910B isbeing monitored. The test port selects a port to monitor to determine ifan optical signal is actually present on the split optical paths and ifso, if the optical path carrying the data in the first optical switchfabric is reliable or has failed. The signals can also be monitored todetermine what is the bit error rate through the optical cross-connectswitch 1900. The test port card 1905 steps from path to path to samplethe signals on the paths to determine where a failure may occur. Thetest port card can use an algorithm such as a round robin algorithm totest each path in sequence. If a faulty path is detected, the test portcard raises an alarm and the information is sent to a network managementsystem, for further fault isolation and servicing of the failure. Thetest port 1905 can also ping-pong from one optical switch fabric toanother in order to alternate the testing process. In FIG. 19A, thesecond optical switch fabric 1910B is being monitored by the opticalpath 1926 using a first test input port. Referring momentarily to FIG.20, the first optical switch fabric 1910A is being monitored by theoptical path 1925 using a second test input port as opposed to thesecond optical switch fabric 1910B to illustrate the ping-pong betweenoptical switch fabrics. Either of the test port cards 1905 and 2005 canstep from path to path to sample the signals over the optical paths todetermine where a failure may occur. If a faulty optical path isdetected, an alarm is signaled and it is removed from available paths inthe respective optical switch fabric until its repaired or the redundantoptical switch fabric is selected to replace the failing path.

Referring now to FIGS. 19A and 20, the test port/monitor card 1905illustrated in FIG. 19A monitors incoming optical signals for eitheroptical switch fabric. The test port/monitor card 2005 illustrated inFIG. 20 can monitor incoming optical signals from either optical switchfabric as well as generate its own optical test signal to activelyself-test optical paths through the either optical switch fabric. Inaddition to the O/E 1917 and the optical switch 1919, the testport/monitor card 2005 includes an electrical to optical converter (E/O)1918 (i.e. a semiconductor laser) to generate an optical test signalwhich is controlled to actively test optical paths through the first andsecond optical switch fabrics. The test port/monitor cards 1905 and 2005can be used in any configuration of an optical cross-connect switchincluding the single and dual optical switch fabric embodimentsdisclosed herein.

The present invention is thus described and as one of ordinary skill cansee, it has many advantages over the prior art. One advantage of thepresent invention is that the costs of regenerating signals within anoptical cross-connect switch can be reduced by utilizing one O/E/O inthe input path or output path of a smart port card of the presentinvention. Another advantage of the present invention is thatnon-intrusive monitoring can be performed on the incoming opticalsignals using the present invention. Still another advantage of thepresent invention is that self-testing of an optical cross-connectswitch can be performed.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art. For example, the presentinvention has been described in detail using an optical cross-connectswitch. However, the present invention may be implemented into otheroptical network equipment that accept optical data signals including anoptical bridge, an optical router, an optical hub, an optical node, anoptical concentrator, or other networking equipment accepting a datasignal embodied in an optical signal. Additionally, it is possible toimplement the present invention or some of its features in hardware,firmware, software or a combination thereof where the software isprovided in a processor readable storage medium such as a magnetic,optical, or semiconductor storage medium.

1. A method of regenerating optical signals in an all-opticalcross-connect switch, the method comprising: providing one or more smartport cards, each of the one or more smart port cards including anoptical-electrical-optical converter in an optical path, theoptical-electrical-optical converter to convert an input optical signalinto an electrical signal and the electrical signal into an outputoptical signal, the output optical signal being responsive to the inputoptical signal; providing one or more passive port cards, the one ormore passive port cards without an optical-electrical-optical converter;and generating an optical path through an optical switch fabric ofoptical switches for optical signals to flow between the one or moresmart port cards and the one or more passive port cards.
 2. The methodof claim 1 wherein the optical-electrical-optical converter is in theinput optical path of each of the one or more smart port cards; and thegenerating of the optical path through the optical switch fabric couplesthe input optical path of the smart port cards to the output opticalpath of the passive port cards.
 3. The method of claim 1 wherein theoptical-electrical-optical converter is in the output optical path ofeach of the one or more smart port cards; and the generating of theoptical path through the optical switch fabric couples the input opticalpath of the passive port cards to the output optical path of the smartport cards.
 4. The method of claim 1 wherein theoptical-electrical-optical converter monitors the optical signal.
 5. Anapparatus for regenerating optical signals in an all-opticalcross-connect switch, the apparatus comprising: a smart port card, thesmart port card including an optical-electrical-optical converter in anoptical path, the optical-electrical-optical converter to convert aninput optical signal into an electrical signal and the electrical signalinto an output optical signal.
 6. The apparatus of claim 5 wherein theoutput optical signal is substantially similar to the input opticalsignal.
 7. The apparatus of claim 5 wherein theoptical-electrical-optical converter provides wavelength conversion suchthat the output optical signal has substantially similar informationcontent as that of the input optical signal but a differing photonicwavelength.
 8. The apparatus of claim 5 wherein theoptical-electrical-optical converter is in the input optical path of thesmart port card.
 9. The apparatus of claim 5 wherein theoptical-electrical-optical converter is in the output optical path ofthe smart port card.
 10. The apparatus of claim 5 wherein theoptical-electrical-optical converter provides a tap to the electricalsignal to monitor the optical signal.
 11. A method of regeneratingoptical signals in an all-optical cross-connect switch, the methodcomprising: converting a first optical signal into an electrical signal;converting the electrical signal into a second optical signal, thesecond optical signal being responsive to the first optical signal; andforming an optical path through an optical switch fabric of opticalswitches over which optical signals can be transported through theoptical cross-connect switch.
 12. The method of claim 11 wherein theconverting of the first optical signal into the electrical signal andthe converting of the electrical signal into the second optical signalare performed in an input optical path to the all-optical cross-connectswitch.
 13. The method of claim 11 wherein the converting of the firstoptical signal into the electrical signal and the converting of theelectrical signal into the second optical signal are performed in anoutput optical path from the all-optical cross-connect switch.
 14. Themethod of claim 11 wherein the converting of the first optical signalinto the electrical signal and the converting of the electrical signalinto the second optical signal regenerates the first optical signal. 15.The method of claim 11 wherein the converting of the first opticalsignal into the electrical signal allows for monitoring of the firstoptical signal.
 16. The method of claim 11 wherein, the first opticalsignal has a first wavelength and the second optical signal has a secondwavelength differing from the first wavelength.